一种高电流密度下效率不降低的绿光有机电致发光器件

为了提高有机电致发光器件(OLED)在高电流密度下的发光效率, 在以C545T掺杂Alq₃为发光层的有机小分子绿光器件中的发光层与电子传输层之间插入超薄LiF绝缘层.结果表明, 器件的外量子效率随着电流密度的增加始终没有降低, 直至600 mA/cm²时达到最大值 4.79%, 是相同电流密度下的参考器件的外量子效率的7倍.     

插入电荷控制层对蓝色OLED发光性能的提高

用蓝色有机荧光材料N⁶,N⁶,N¹²,N¹²-tetrap-tolylchrysene-6,12-diamine （DNCA）作为发光层,在发光层中间以及发光层与电子传输层之间插入2-methyl-9,10-di（2-napthyl）anthracene （MADN） 和9,10-di（2-naphthyl）anthracene （ADN） 作为电荷控制层,制备了结构为ITO/NPB（40 nm）/DNCA（15 nm）/MADN（3 nm）/DNCA（15 nm）/ADN（3 nm）/Bphen（30 nm）/LiF（0.8 nm）/Al（120 nm）的蓝色有机电致发光器件（OLED）。该器件的最大电流效率和最大亮度分别为5.6 cd/A和23 310 cd/m²。与传统的单发光层器件相比,最大电流效率和最大亮度分别提高了70%和87%。器件发光性能的提高可归结于两个电荷控制层在整个器件中的协同作用。第一电荷控制层MADN的作用主要是将发光层区域分成两个部分,从而扩大了激子在发光层中的复合区域;第二电荷控制层ADN可以有效地将空穴限制在发光层中,避免了激子在电子传输层中形成的无辐射跃迁从而提高了器件的发光性能。     

DPVBi为激子阻挡层的亚单层有机发光器件的制备与光电性能研究

结合亚单层的有机发光技术,制备了一种多层有机电致发光器件,其结构为ITO/m-MTDATA (50nm)/ C545T (0.05nm) /DPVBi (d nm)/DCM2(0.05nm)/ Alq (60nm) /LiF(1nm) /Al.荧光材料C545T和DCM2以亚单层的方式插入DPVBi前后,通过改变DPVBi的厚度,观察器件性能的变化,当DPVBi为4 nm时,器件在4V电压下最大发光效率是4.19 cd/A,在13 V电压下最大亮度是17050 cd/m2.分析对比了四种不同厚度器件的电流密度-电压曲线、亮度-电压曲线、电致发光光谱图和色坐标,发现选择合适厚度的激子阻挡层,可以得到效率较高的器件.激子阻挡层一般选择载流子传输能力较差,HOMO能级较低的材料.所得结果对有机发光器件尤其是采用亚单层有机白光器件的设计和制作有一定的指导作用.     

LiF超薄层引起的OLEDs发光光谱展宽

将LiF插入到发光层Alq₃中,制备了有机电致发光器件(OLED),其器件的结构为:ITO/NPB (45 nm)/Alq₃ (x nm)/LiF (0.3 nm)/Alq₃ /Al(150 nm)。发现器件的电致发光谱(Electroluminescence spectra, EL)有非常明显的展宽现象,这为白光器件的制备提供了一条简单的途径。通过对比LiF在Alq₃中不同厚度处的发光谱,发现在x=10时谱线展宽最显著,器件最大亮度在22 V时达到8 260 cd/m²,最大效率可达 4.83 cd/A,并对其光谱展宽的机理及器件特性进行了分析。     

有机电致发光器件中观察到的三重态-三重态湮灭导致的荧光发射

在高浓度DMQA掺杂于Alq₃作为发射层的器件中直接观察到了超线性的发射增强现象.当DMQA的浓度在1.6%~5.6%之间时,电流密度大于300mA/cm²,电致发光效率随电流密度的增大而增加.这是由于在重掺杂器件中,较多的染料有效的转移了Alq₃中的激子,降低了器件中的非辐射损失,同时,三重态-三重态湮灭过程产生了新的单重态激子,贡献了额外发光的结果.当后者的贡献大于器件中的非辐射损失时,器件的发光效率将随电流的增大而上升.     

含新型噁二唑类电子传输层的有机发光二极管性能研究

含吡啶基的噁二唑类材料(PDPyDP)作为一种新型的电子传输层被有效地应用于可溶性聚对苯乙炔(MEHPPV)为发光层的双层结构的有机发光二极管器件中,并将其光电性能与MEHPPV的单层结构器件及分别含苯环(PDPDP)和反1,2亚乙烯基(PDVDP)的另外两种二唑类电子传输层的双层结构器件进行比较.EL光谱测量表明,它们的发光均来自于MEHPPV层,而它们相似的器件电流和光输出随驱动电场变化的规律表明这些器件中相似的电荷转移过程,但电致发光阈值电场对于双层结构器件来说低于单层结构器件,而插入PDPyDP层的器件,其阈值电场最低.在电流密度为50mA/cm²时,单层器件及各插入PDVDP、PDPDP和PDPyDP的双层器件的外量子效率相对值分别为3×10^-3%,5×10^-3%,2×10^-2%和0.1%.并分析了插入PDPyDP使器件发光性能提高最为明显的原因.通过将此类器件的结构等作进一步优化,其最佳量子效率可高达1.44%.     

不同电极对蓝光有机电致发光器件性能的影响

利用高真空多源型有机分子沉积系统分别制备了不同负电极为Al、LiF/Al和Mg:Ag的有机小分子多层电致发光器件,比较了不同负极对以五苯基环戊二烯（PPCP）为发光层的蓝光有机电致发光器件性能的影响,发现以LiF/Al作负极的器件在综合性能上优于其它器件。其中器件ITO／TPD／PPDP／Alq/LiF/Al蓝光发射的最大发光亮度达2375cd/m^2,最大发光效率为0.26lm/W.     

磁场对有机电致发光的影响

制备了常规有机发光二极管ITO/NPD/Alq₃/LiF/Al，测量了该器件发光的磁场效应.发现尽管在1T范围内的磁场对发光层Alq₃的光致发光没有影响，但磁场作用下器件的电致发光(MEL)却呈现出明显的磁效应，且MEL与器件的偏压有很强的依赖关系：在小偏压时，随着磁场的增加MEL是单调递增，且在大小约为40kA/m的磁场下达到饱和，之后即使磁场增大到约1T 的情况下也没有变化；但当偏压变大时，MEL则呈现先增加，在40kA/m处达到峰值后却又减弱，而且偏压越大该MEL的减弱则越明显.对所观察到的实验结果进行了定形解释，即三线态激子相互淬灭产生单线态激子和三线态激子与器件中的非平衡载流子相互作用是此效应的物理机理. 关键词： 有机发光 磁场效应 激子淬灭     

磁场对基于Co铁磁薄膜的有机发光器件效率和电流的影响

制备结构为ITO/Co/NPB/Alq₃/LiF/Al的有机发光器件,测量了室温下磁场对器件发光效率和电流的影响.发现磁场强度小于80 mT时,器件发光效率随磁场强度的增加而增大,最大为18.8%,随磁场强度的继续增加发光效率的增强趋于饱和.效率的增加是Co的自旋极化的注入和磁场效应共同作用的结果,其中自旋极化注入起主要作用.在磁场强度小于60 mT时电流随磁场增强而增加,最大为6.9%,随磁场强度的进一步增加电流的增加有所减弱.产生这种现象的原因可归结为磁场相关的单线态极化子对的解 关键词： 有机电致发光 自旋极化 磁场效应     

有机/有机界面污染对有机电致发光器件稳定性的影响(英文)

有机电致发光器件的稳定性是其实用化面临的主要难题之一。为了研究有机/有机界面性质对有机电致发光器件稳定性的影响,采用溶液旋涂的NPB(NPBSC)作为器件的空穴传输层制备了两种异质结电致发光器件:ITO/NPBSC/Alq3/LiF/Al和ITO/NPBSC/NPB/Alq3/LiF/Al,对比研究了器件的发光性能和工作稳定性。研究结果表明:完全使用NPBSC作为空穴传输层的器件性能和稳定性都较差,这归因于不稳定的NPBSC/Alq3界面,在空气中旋涂制备NPB层时,空气中的水蒸气和氧气分子会粘附在空穴传输层表面,这样就会引起界面处Alq3分子的发光猝灭。插入10 nm真空蒸镀的NPB层可以显著地提高器件的发光性能和稳定性,10 nm的NPB层把污染界面与激子复合区界面分开,避免了水蒸气和氧气分子对Alq3分子的发光猝灭,器件的效率增加了1.15 cd/A,半衰期寿命提高了4倍。     

Silver‐Based Nanoparticles for Surface Plasmon Resonance in Organic Optoelectronics

Organic optoelectronic devices including organic light‐emitting diodes (OLEDs) and polymer solar cells (PSCs) have many advantages, including low‐cost, mechanical flexibility, and amenability to large‐area fabrication based on printing techniques, and have therefore attracted attention as next‐generation flexible optoelectronic devices. Although almost 100% internal quantum efficiency of OLEDs has been achieved by using phosphorescent emitters and optimizing device structures, the external quantum efficiency (EQE) of OLEDs is still limited due to poor light extraction. Also, although intensive efforts to develop new conjugated polymers and device architectures have improved power conversion efficiency (PCE) up to 8%–9%, device efficiency must be improved to >10% for commercialization of PSCs. The surface plasmon resonance (SPR) effect of metal nanoparticles (NPs) can be an effective way to improve the extraction of light produced by decay of excitons in the emission layer and by absorption of incident light energy within the active layer. Silver (Ag) NPs are promising plasmonic materials due to a strong SPR peak and light‐scattering effect. In this review, different SPR properties of Ag NPs are introduced as a function of size, shape, and surrounding matrix, and review recent progress on application of the SPR effect of AgNPs to OLEDs and PSCs.     

Tandem organic light-emitting diode with a molybdenum tri-oxide thin film interconnector layer

A 10-nm-thick molybdenum tri-oxide(MoO3) thin film was used as the interconnector layer in tandem organic lightemitting devices(OLEDs).The tandem OLEDs with two identical emissive units consisting of N,N-bis(naphthalen-1-yl)N,N-bis(phenyl)-benzidine(NPB) /tris(8-hydroxyquinoline) aluminum(Alq3) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices.At 20 mA/cm2,the current efficiency of the tandem OLEDs using the interconnector layers of MoO3 thin film was about 4.0 cd/A,which is about twice that of the corresponding conventional single-unit device(1.8cd/A).The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200cd/m2.The experimental results demonstrated that a MoO3 thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs.Such an interconnector layer can be easily fabricated by simple thermal evaporation,greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers.A possible explanation was proposed for the carrier generation of the MoO3 interconnector layer.     

Co50Fe50-xSix合金的结构相变和磁性

利用实验测量和理论计算相结合的方法,研究了介于B2结构CoFe低有序合金和L2₁结构Co₂FeSi高有序合金之间的Co₅₀Fe_50-xSi_x合金的结构相变、磁相变、分子磁矩和居里温度.采用考虑Coulomb相互作用的广义梯度近似(GGA+U)方法计算了合金的能带结构.研究发现,合金出现较强的原子有序倾向,表现出较强的共价成相作用.合金的晶格常数、磁矩、居里温度随Si含量的增加而线性地降低,极限成分Co₂FeSi合金的分子磁矩和居里温度分别达到5.92μ_B和777 ℃.原子尺寸效应导致合金晶格发生变化,但并未成为居里温度和分子磁矩变化的主导因素.分子磁矩的变化符合Slater-Pauling原理,但发现原子磁矩的变化并非线性,据此提出了共价成相对磁性影响的观点.采用Stearns理论解释了居里温度的变化趋势,排除了原子间距对居里温度的主导影响作用.能带计算的结果还表明,Co₂FeSi作为半金属材料并非十分完美,可能在实际应用中会出现自旋极化率降低的问题.发现该系列合金的结构相变和磁相变随着成分的变化聚集在窄小的成分和温度范围内. 关键词： 磁性 Heusler合金 结构相变     

高效率的有机电致发光器件

有机电致发光器件 (OL EDs)的发光机理包括电子和空穴从电极的注入、激子的形成及复合发光 ,其中 ,空穴和电子的注入平衡是非常重要的。为了平衡载流子的注入以得到高效率和稳定性好的器件 ,人们不仅使用了电子注入更为有效的 L i F/ Al[1] 和 Cs F/ Al[2 ] 等复合电极 ,同时也使用了空穴缓冲层 ,如 S.A.Van Slyke等 [3]在ITO和 NPB之间使用 Cu Pc,使得器件的稳定性得到了明显的提高 ;A.Gyoutoku等[4 ] 用碳膜使器件的半寿命超过 3 5 0 0小时 ;最近 ,Y.Kurosaka等 [5]和 Z.B.Deng[6 ]分别在 ITO和空穴传输层之间插入一薄层 Al…     

利用氧等离子体处理阳极银实现高效率顶发射有机电致发光

主要报道在器件结构为玻璃衬底/Ag(阳极)/NPB(空穴传输层)/Alq3(电子传输及发光层)/Sm(半透明阴极)/Alq3的顶发射有机电致发光器件中,利用氧等离子体对阳极银的表面进行处理来降低阳极和空穴传输层(Ag/NPB)界面处的空穴注入势垒,提高顶发射有机电致发光器件的性能。主要研究了氧等离子体处理时间对阳极银和顶发射有机电致发光器件光电特性的影响。紫外光电子能谱表明,氧等离子体处理能有效降低Ag/NPB界面处的空穴注入势垒。通过优化处理时间获得最佳器件性能,优化后的器件最大效率可达6.14cd/A。     

Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer

The efficiency of organic light-emitting devices (OLEDs) based on N,N'-bis(1-naphthyl)-N,N'-diphenyl-N,1'-biphenyl-4,4'-diamine (NPB) (the hole transport layer) and tris(8-hydroxyquinoline) aluminum (Alq₃) (both emission and electron transport layers) is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm², which is about 86% higher than that of an ordinary device (without a LiF interlayer, 3.2 cd/A). An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.     

Tandem organic light-emitting diode with molybdenum tri-oxide thin film interconnector layer

A 10-nm thickness molybdenum tri-oxide (MoO₃) thin film was used as the interconnector layer in tandem organic light-emitting devices (OLEDs). The tandem OLEDs with two identical emissive units consisting of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB)/tris(8-hydroxyquinoline) aluminum (Alq₃) exhibited current efficiency-current density characteristics superior to the conventional single-unit devices. At 20 mA/cm², the current efficiency of the tandem OLEDs using the interconnector layers of MoO₃ thin film was about 4.0 cd/A, which is about twice of that of the corresponding conventional single-unit device (1.8 cd/A). The tandem OLED showed a higher power efficiency than the conventional single-unit device for luminance over 1200 cd/m². The experimental results demonstrated that a MoO₃ thin film with a proper thickness can be used as an effective interconnector layer in tandem OLEDs. Such an interconnector layer can be easily fabricated by simple thermal evaporation, greatly simplifying the device processing and fabrication processes required by previously reported interconnector layers. A possible explanation was proposed for the carrier generation of the MoO₃ interconnector layer.     

Exciplex elimination in an organic light-emitting diode based on a fluorene derivative by inserting 4,4’-N,N’-dicarbazole-biphenyl into donor/acceptor interface

Organic light-emitting diodes (OLEDs) composed of a novel fluorene derivative of 2,3-bis(9,9-dihexyl-9H-fluoren-2-yl)-6,7-difluoroquinoxaline (F2Py) were fabricated, and exciplex emission was observed in the device. To depress the exciplex in an OLED for pure colour light emission, 4, 4'-N,N'-dicarbazole-biphenyl (CBP) was inserted as a separator at the donor/acceptor interface. It was found that the device without the CBP layer emitted a green light peaking at 542~nm from the exciplex and a shoulder peak about 430~nm from F2Py. In contrast, the OLED with CBP layer emitted only a blue light peak at about 432~nm from F2Py. Device efficiencies were calculated by a simulative mode in an injection controlled type mechanism, and the results showed that exciplexes yield much lower quantum efficiency than excitons. The device with CBP has a higher power efficiency as no exciplex was present.     

互混型有机电致发光器件

通过共蒸镀空穴传输材料TPD和电子传输材料Alq₃,在普通双层器件的异质结界面引入了均匀互混层,并研究了互混层的厚度变化对器件光电性能的影响。互混层的引入在一定程度上改善了普通双层器件的异质结界面由于高浓度载流子积聚导致的高电场和界面缺陷对器件主要性能(效率和寿命)的负面影响。我们发现一定厚度的互混层使器件的性能有所提高。